1. Field of the Invention
The present invention relates to a wing panel and an aircraft main wing provided with the said wing panel.
2. Description of the Related Art
An aircraft main wing is formed by attaching a wing panel forming the outer surface of the main wing to a frame member forming a skeleton. The wing panel is curvedly formed into a three-dimensional shape. Specifically, in an airframe, for example, such that an engine is attached to the lower part of the main wing, the wing panel forming the upper surface of main wing is curvedly formed so that the outer surface side of main wing is convex in the spanwise direction of the wing, and the wing panel forming the lower surface of main wing is curvedly formed so that the outer surface side of main wing is concave in the spanwise direction of the wing (convex upwardly).
To curvedly form such a wing panel, various methods including the peen forming method have been used (for example, refer to Takeshi Yamada et al. “Development of Shot Peening for Wing Integral Skin for Continental Business Jets” Mitsubishi Heavy Industries Technical Review, Vol. 39, No. 1 (2002), p. 36).
Among these methods, the peen forming method is a method in which metal shots are projected from one side of the wing panel or a member provided integrally with the wing panel to stretch the surface of a portion with which the metal shots collide, and the wing panel is curvedly formed by the difference in arc length between the one side and the other side on which the surface is not stretched.
For example, for the wing panel forming the upper surface of main wing, metal shots are projected to the side of the outer surface of main wing along a stringer. By doing this, the outer surface side of main wing is stretched in the spanwise direction of the wing. On the other hand, the inner surface side of main wing is not stretched by the collision of metal shots. As a result, the wing panel is curvedly formed so that the outer surface side of wing panel becomes convex in the spanwise direction of the wing on account of the difference in arc length between the stretched outer surface side and the not-stretched inner surface side.
As shown in FIG. 5, on a wing panel 1 forming the lower surface of main wing, a rib-shaped stringer member 2, which is continuous in the spanwise direction of main wing, is attached to the side of the inner surface of main wing. By projecting metal shots to a portion near a tip end part 2a of the stringer member 2, the stringer member 2 is formed so that the tip end part 2a side stretches with respect to a base part 2b fixed to the wing panel 1. As a result, the wing panel 1 is curvedly formed so that the inner surface side (the side on which the stringer member 2 is provided) of main wing is convex in the spanwise direction of the wing.
Unfortunately, in the case where the main wing of a small aircraft is formed by the peen forming method, the radius of curvature of main wing is small. In particular, for an airframe such that an engine is attached to the lower part of the main wing, for the wing panel forming the lower surface of main wing, to provide a clearance between the engine and the ground, the radius of curvature is small in a portion that is curvedly formed so that the wing panel is convex upward in the spanwise direction of the wing around the engine.
In such a case, there arise problems such as a problem that the wing panel 1 is not curved sufficiently by merely peen forming a portion near the tip end part 2a of the conventional stringer member 2, so that the forming work requires much time. Therefore, the improvement in formability has been demanded.